1. Saltwater Crocodile
The saltwater crocodile, which can grow to be over 20 feet long, is known for being aggressive toward humans. Death counts are not well known because reports are suspect, and there is no reporting in much of the saltwater crocodile’s range. At all costs, avoid!
Note: The Fisheries Blog compiled this list, which is not exhaustive of dangerous sea creatures, nor is it in any order from least to most dangerous. As with any dangerous animal, take precautions—know what risks may exist in the area, obey all posted warnings, and seek medical attention if you come across one. Fortunately, many dangerous sea creatures, like most other animals, will avoid you just as much as you will avoid them.
2. Box Jelly
This group contains several deadly species, including the Irukandji jellyfish, sea wasps, and common kingslayers (pictured above). These jellies, which can kill humans in less than 5 minutes, are found in the Indo-Pacific region, though some species are found elsewhere.
3. Blue-ringed Octopus
This octopus, with its distinctive blue circles, carries tetrodotoxin, a venom that stops your breathing and is 1,200 times more toxic than cyanide. Fortunately, the octopus is not aggressive and will likely avoid you before you can.
4. Cone Snail
Avoid these snails at all costs, no matter how beautiful their shells are. These snails carry their own venom, conotoxin, whose effects are severe and not fully understood.
5.Sea Snake
These venomous sea snakes, known as kraits, are members of the cobra family of snakes. The good news is that they are not aggressive and have very small mouths, so the likelihood of being bitten is extremely low.
